This application relates to chemical mechanical planarization of semiconductor wafers. More particularly, this application relates to a modified platen assembly for providing improved wafer removal profile performance in a linear or rotary polishing system.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor wafer is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. This sensitivity is accentuated with the current drive for smaller, more highly integrated circuit designs which cannot tolerate certain nonuniformities within a particular die or between a plurality of dies on a wafer. Because semiconductor circuits on wafers are commonly constructed in layers, where a portion of a circuit is created on a first layer and conductive vias connect it to a portion of the circuit on the next layer, each layer can add or create nonuniformity on the wafer that must be smoothed out before generating the next layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad moving in the plane of the wafer surface to be planarized. The polishing pad is typically disk or a belt. In some systems, a polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer. In other CMP systems, a fixed-abrasive polishing pad is used to polish the wafer. In fixed-abrasive applications, the wafer holder presses the wafer against the rotating fixed-abrasive polishing pad, deionized water (or some other non-abrasive substance) is applied, and the pad is moved to polish and planarize the wafer.
In linear wafer polishers, a support assembly is often positioned under the linear belt to provide additional support and polishing control to the polishing process taking place on the opposite side of the linear belt. Examples of linear belt supports are shown in U.S. Pat. No. 5,593,344 where one or more fluid bearings are used to support the belt. One objective of the fluid bearings is to help control the wafer removal profile of the linear polisher by adjusting the fluid pressure applied to various zones underneath the belt. Despite the wafer removal profile control that can be achieved with the fluid bearings, some wafer removal variations may remain that require additional compensation. Accordingly, there is a need for an improved mechanism for supporting a linear belt or a rotary pad.
In order to address the need for improved wafer removal profile, a platen for use in a platen assembly for supporting a polishing member, such as a linear belt on a linear polishing apparatus, or a rotary pad on a rotary polishing apparatus, is described below. According to one aspect of the invention, a platen assembly for supporting a polishing member on a polishing apparatus is disclosed that has a platen comprising a substantially planar surface with a leading edge and a trailing edge, where the trailing edge is positioned at an opposite end of the substantially planar surface from the leading edge. A plurality of fluid channels is disposed between the leading and trailing edges of the platen, each of the fluid channels defines a respective opening in the substantially planar surface. At least one region of altered topography is positioned on the platen, where each of the at least one region of altered topography includes one of a region of raised of raised topography and a region of lowered topography relative to the substantially planar surface.
According to another aspect of the invention, the platen assembly includes the platen having a segmented platen ring positioned around a portion of the planar surface. Each segment may be positioned to be a raised or lowered region of topography.
According to another aspect of the invention, a linear belt support assembly for supporting a linear belt, wherein a wafer having a diameter is pressed against one side of the linear belt, includes a platen. The platen includes a substantially planar surface positioned underneath the linear belt opposite the wafer. The substantially planar surface is positioned in the linear belt support assembly and has a diameter that is greater than the diameter of the wafer. The platen further includes a leading edge and a trailing edge, where the trailing edge is positioned at an opposite end of the substantially planar surface from the leading edge. Also a plurality of fluid channels are disposed between the leading and trailing edges of the platen, where each of the fluid channels is a respective opening defined by the substantially planar surface. At least one region of raised topography is positioned on the platen closer to the trailing edge than to the leading edge.